Fix for #233 (final part)

mysql-test/r/gis.result:
  test result added
mysql-test/t/gis.test:
  test case added
sql/field.h:
  now set_field_to_null can return -1
sql/field_conv.cc:
  now set_field_to_null* can return -1

mysql-test/r/gis.result

@@ -458,3 +458,9 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 Warnings:
 Note	1003	select high_priority issimple(multipoint(point(3,6),point(4,10))) AS `issimple(MultiPoint(Point(3, 6), Point(4, 10)))`,issimple(point(3,6)) AS `issimple(Point(3, 6))`
+create table t1 (a geometry not null);
+insert into t1 values (GeomFromText('Point(1 2)'));
+insert into t1 values ('Garbage');
+ERROR HY000: Unknown error
+alter table t1 add spatial index(a);
+drop table t1;

mysql-test/t/gis.test

@@ -160,3 +160,11 @@ SELECT SRID(GeomFromText('LineString(1 1,2 2)',101));
 explain extended SELECT SRID(GeomFromText('LineString(1 1,2 2)',101));
 #select issimple(MultiPoint(Point(3, 6), Point(4, 10))), issimple(Point(3, 6)),issimple(PolygonFromText('POLYGON((10 10,20 10,20 20,10 20,10 10))')),issimple(GeometryFromText('POINT(1 4)')), issimple(AsWKB(GeometryFromText('POINT(1 4)')));
 explain extended select issimple(MultiPoint(Point(3, 6), Point(4, 10))), issimple(Point(3, 6));
+
+create table t1 (a geometry not null);
+insert into t1 values (GeomFromText('Point(1 2)'));
+-- error 1105
+insert into t1 values ('Garbage');
+alter table t1 add spatial index(a);
+
+drop table t1;

sql/field.h

@@ -1184,8 +1184,8 @@ Field *make_field(char *ptr, uint32 field_length,
 		  struct st_table *table);
 uint pack_length_to_packflag(uint type);
 uint32 calc_pack_length(enum_field_types type,uint32 length);
-bool set_field_to_null(Field *field);
-bool set_field_to_null_with_conversions(Field *field, bool no_conversions);
+int set_field_to_null(Field *field);
+int set_field_to_null_with_conversions(Field *field, bool no_conversions);
 bool test_if_int(const char *str, int length, const char *int_end,
 		 CHARSET_INFO *cs);
 

sql/field_conv.cc

@@ -109,7 +109,7 @@ static void do_outer_field_to_null_str(Copy_field *copy)
 }
 
 
-bool
+int
 set_field_to_null(Field *field)
 {
   if (field->real_maybe_null())
@@ -149,7 +149,7 @@ set_field_to_null(Field *field)
 		If no_conversion was not set, an error message is printed
 */
 
-bool
+int
 set_field_to_null_with_conversions(Field *field, bool no_conversions)
 {
   if (field->real_maybe_null())